FIG. 1 is an exploded perspective view of an external communication jack of a mobile terminal in accordance with the related art. FIG. 2 is a sectional view illustrating a state where a plug of an earphone is insertedly positioned in the external communication jack in accordance with the related art.
The related art external communication jack 110 includes a body 106 mounted in a printed circuit board (PCB) 102 of a mobile terminal and an insertion passage 108 formed at its central portion, into which a plug 104 of an earphone is inserted. Platy connection terminals 120a, 120b and 120c are mounted at certain intervals in the insertion passage 108 of the body 106, which are soldered to the PCB 102 so as to be electrically operational with a bar-type connection part 138 of the plug 104. An annular connection terminal 122 is mounted at a front side of the body 106, into which an annular connection part 130 of the plug 104 is inserted.
The plug 104 of the earphone includes a plug body 132 to which a wire is connected. First, second and third connection portions 134a, 134b and 134c, respectively, extend from the plug body 132 and are sequentially formed at certain intervals with an insulation layer 136 positioned as a boundary therebetween. The annular connection part 130 is mounted at the plug body 132 and formed in a ring shape with a certain interval at an outer circumferential surface of the bar-type connection part 138.
The platy connection terminals 120a, 120b and 120c which contact the bar-type connection part 138 in the insertion passage 108 are sequentially mounted at the body 106, and a cylindrical terminal mounting part 140 is formed at the front side of the body 106, on which the annular connection terminal 122 is mounted.
The first connection terminal 120a elastically contacts the first connection portion 134a. The second connection terminal 120b is disposed at a certain distance from the first connection terminal 120a and contacts the second connection portion 134b. The third connection terminal 120c is disposed at a certain distance from the second connection terminal 120b and contacts the third connection portion 134c. 
The annular connection terminal 122 is formed at the outer circumference of the terminal mounting part 140. A connection plate 142 for transmitting an electrical signal is integrally connected to the PCB 102 by soldering or the like. Specifically, the connection plate 142 is formed as a thin plate type, integrally extends from a rear side of the annular connection terminal 122, is fixed to the body 106, and is connected to the PCB 102 by soldering or the like.
When the plug 104 is mounted to the conventional external communication jack 110, the bar-type connection part 138 of the plug 104 is inserted into the insertion passage 108 and the annular connection part 130 is mounted at the outer circumference of the annular connection terminal 122.
Moreover, the first connection portion 134a of the bar-type connection part 138 contacts the first connection terminal 120a mounted inside the insertion passage 108, the second connection portion 134b contacts the second connection terminal 120b, and the third connection portion 134c contacts the third connection terminal 120c. As stated above, the annular connection part 130 is mounted at the outer circumferential surface of the annular connection terminal 122. Thus, an electrical signal of the mobile terminal can be transmitted to the earphone or an electrical signal of the earphone can be transmitted to the mobile terminal.
However, the related art external communication jack has the following problems.
In a state where the plug 104 is mounted in the external communication jack 110, when the plug 104 is rotated by a user, the annular connection part 130 positioned at the annular connection terminal 122 will also be rotated. Accordingly, a rotational moment is generated at the annular connection terminal 122. This is problematic because a connection portion between the annular connection terminal 122 and the connection plate 142 can be damaged as a result of the generated rotational moment. Moreover, the soldered portion between the connection plate 142 and the PCB 102 can be damaged.
Specifically, when the plug 104 is rotated while being insertedly positioned in the external communication jack 110, because the annular connection part 130 of the plug 104 is elastically installed at the annular connection terminal 122, the rotational force of a rotated annular connection part 130 is transferred to the annular connection terminal 122 to continuously generate a rotational moment at the annular connection terminal 122. This damages a portion between the annular connection terminal 122 and the connection plate 142 and may further damage a soldered portion between the PCB 102 and the connection plate 142.